1. Field of the Invention
The present invention relates to a manufacturing method of a display apparatus, particularly to a manufacturing method of a display apparatus which comprises a display panel in which a plurality of display pixels having a light emission device in which a carrier transport layer is formed by applying a liquid material including a carrier transporting material are two-dimensionally arranged.
2. Description of Related Art
In recent years, a display device which comprises a display panel (organic EL display panel) in which organic electroluminescent devices (hereinafter, abbreviated as “organic EL device”) which are self light emitting elements are two-dimensionally arranged is know as the display device for electronic devices such as a cell phone, a portable music player and the like. Particularly, the display response rate is faster and the view angle dependence is smaller in the organic EL display panel of an active matrix drive type comparing to the widely used liquid display apparatus, and also the backlight, the light guide plate or the like which is required in the liquid crystal display apparatus is not needed in the organic EL display panel. Therefore, there is a possibility that the organic EL display panel can be even thinner and lighter. Thus, the organic EL display panel is expected to be used in various types of electronic devices in the future.
Here, as widely known, the organic EL device has a device structure in which the anode (positive) electrode, the organic EL layer (light emitting function layer) and the cathode (negative) electrode are orderly layered in a stacking manner on one side of glass substrate or the like. Further, the organic EL device emits light (excitation light) based on energy generated when holes and electrons which are injected are recombine in the organic EL layer by applying positive voltage to the anode electrode and negative voltage to the cathode electrode so as to exceed the light emission threshold in the organic EL layer. The organic EL device can be classified in the organic EL device of low molecular system and the organic EL device of high molecular system according to the organic material (hole transporting material and electron transporting material) which forms the carrier transport layer which becomes the organic EL layer.
In case of the organic EL device which uses the organic material of low molecular system, the deposition method is used in the manufacturing process in general. When the organic film of low molecular system is being selectively formed only on the anode electrode of the pixel forming region, a mask for preventing the deposition of the low molecular material to the region other than the anode electrode is used, and there is a problems that the material loss at the time of manufacturing is great because the low molecular material also attaches on the surface of the mask and that the manufacturing process is inefficient.
On the other hand, in case of the organic EL device which uses the organic material of high molecular system, the inkjet method (liquid drop discharging method), the nozzle printing method (liquid flow discharging method) or the like can be applied as the wet type film forming method in general. Therefore, the solution of the above organic material can be selectively applied only to the anode electrode or to the specified region including the anode electrode. Thus, the thin film of the organic EL layer (the hole transport layer, the electron transport layer, the light emission layer and the like) can be formed in a great accuracy by the effective manufacturing process in which the material loss is small.
In such organic EL display panel of high molecular system, there is known an organic EL display panel having a panel structure in which a partition wall which is continuously formed and which protrudes on the insulative substrate is provided between each pixel forming regions in order to prevent the phenomenon in which the mixing of colors (color mixing) of the light emitting colors occurs between in display pixels by the light emitting material in different colors being mixed into the adjacent pixel forming regions when the forming region (pixel forming region) of each display pixel to be arranged on the insulative substrate is being defined and when the liquid material including the organic material of high molecular system is being applied. Such organic EL display panel comprising the partition wall is described in detail in JP2001-76881A, for example.
However, in the above described organic EL device of high molecular system or in some of the organic EL device of low molecular system, there is a problem that mixing (color mixing) of the light emitting colors occur between the display pixels by the light emitting material of different colors mixing into the adjacent pixel forming regions or there is a problem that the film thickness of the organic EL layer which is formed in the pixel forming region is uneven due to the surface tension, the cohesion force and the like when the organic EL layer (the hole transport layer, the electron transport layer, and the light emission layer) is being manufactured by using the wet film forming method such as the inkjet method, the nozzle printing method or the like. The surface tension, the cohesion force and the like are caused by the characteristic (the lyophilic characteristic and the repellency characteristic) of the surface of each pixel forming region in which the liquid material including the organic material is applied, the surface of the partition wall provided between each display pixels (pixel forming region) and the solvent component of the liquid material (embrocation).
Therefore, when the organic EL device operates so as to emit light, deterioration of the organic EL layer (organic EL device) is significant due to the light emission drive current concentrates to flow in the area where the film thickness of the organic EL layer is thin, and there are problems that the reliability of the display panel and the life span of the device are reduced, the desired brightness cannot be obtained because the voltage at the start of light emission is changed (shifted) from the designed value, and the display image quality of the display panel is degraded.